The overall objective of this proposal is to continue to investigate cellular, molecular, and electrophysiologic mechanisms by which retinoids induce the differentiation and modulate the immunocompetence of human lymphocytes. The first aim is to determine the T-cell spectrum of action and mechanism by which retinoic acid (RA) regulates IL-2-receptor (IL-2R) expression on T lymphoblasts. Our previous studies with thymocyte blasts have led us to speculate that T-cell responses to RA are dependent upon suboptimal IL-2 utilization. Experiments have been designed to address this question as well as to delineate the level of regulation by which RA affects IL-2R gene expression. The second aim of this project is to establish role for ion channels in early "triggering" events in RA immunomodulation of human B-cell hybridomas. These electrophysiological investigations will utilize the "patch-clamp" methodology and focus on two fundamental questions: 1) Does RA modulate ion (Ca) channels in the hybridoma cells? 2) Is the ability of RA to alter ion channels involved in its differentiation-inducing activity. Results obtained will provide basic information concerning the role of ion channels and ion fluxes in the immunoregulatory processes of B cells. Thirdly, we propose to expand our studies of retinoid effects on human B cells by delineating the interrelationship between RA immune modulation and normal developmental drives. Based upon our work with T lymphocytes, it is our hypothesis that RA does not act as a direct differentiation drive on B cells, but rather alters their sensitivity to norm a1 developmental signals/growth factors. This hypothesis will be tested by assessing the effects of RA along with various activation\growth signals on the differentiation and the secretion from fresh tonsil lymphocytes. Results obtained will be complementary to the more basic ion-related questions that are being addressed with the B-cell hybridomas. Finally, we will delineate the cellular mechanism of action of in vivo 13-cis RA therapy to enhance responses to defined antigens (KLH and tetanus) using patient materials generated during the past funding period. Initial studies indicate a significant retinoid induced enhancement of secondary anti-KLH antibody responses to suboptimal immunizing doses of KLH. Using a variety of in vitro assays, we will discern the T- and B-cell contributions of this effect as well as the retinoid-sensitive phase of the immunization process. This study will, for the first time in humans, characterize the modulation of antigen-specific immune responses by in vivo administration of a retinoid.